 
Summary: Monte Carlo study of phase separation in aqueous protein solutions
Aleksey Lomakin, Neer Asherie, and George B. Benedek
Department of Physics and Center for Materials Science and Engineering,
Massachusetts Institute of Technology, Cambridge, Massachusetts 021394307
Received 11 July 1995; accepted 18 October 1995
The binary liquid phase separation of aqueous solutions of crystallins is utilized to gain insight
into the microscopic interactions between these proteins. The interactions are modeled by a
squarewell potential with reduced range and depth . A comparison is made between the
experimentally determined phase diagram and the results of a modified Monte Carlo procedure
which combines simulations with analytic techniques. The simplicity and economy of the procedure
make it practical to investigate the effect on the phase diagram of an essentially continuous variation
of in the domain 1.05 2.40. The coexistence curves are calculated and are in good agreement
with the information available from previous standard Monte Carlo simulations conducted at a few
specific values of . Analysis of the experimental data for the critical volume fractions of the
crystallins permits the determination of the actual range of interaction appropriate for these
proteins. A comparison of the experimental and calculated widths of the coexistence curves suggests
a significant contribution from anisotropy in the real interaction potential of the crystallins. The
dependence of the critical volume fraction c and the reduced critical energy ^c upon the reduced
range is also analyzed in the context of two ``limiting'' cases; mean field theory ( ) and the
Baxter adhesive sphere model ( 1). Mean field theory fails to describe both the value of c and
